1. Field of the Invention
The present invention relates to a semiconductor structure, especially to a semiconductor structure including a pad structure and a protection structure.
2. Description of the Prior Art
Along with the development of technology and the improvement of the semiconductor techniques, electronic devices are widely used in modern life. Micro-electro-mechanical system (MEMS) technology is to fabricate micro mechanical devices by using conventional semiconductor technologies such as electroplating, etching such that a mechanical component in a micro-meter scale may be formed. The MEMS device may be, for example, the voltage controlling component in an ink printer, the gyroscope in a car to detect the tilt of the car, or the vibration membrane in a microphone to sense a sound. The MEMS technology which combines the fabrication process of the mechanical and the electronic devices has the advantages of low cost, high performance and high density.
At present, the MEMS is usually integrated into a chip in a form of system on chip (SOC), especially a chip fabricated by a conventional CMOS process. For instance, a MEMS region and a CMOS region may be formed on a die simultaneously. In the present fabrication method to integrate the CMOS region and the MEMS region, many problems may occur. For example, when fabricating the CMOS and the MEMS devices, the influence of fabrication methods between each region may be occurred.
Please refer to FIG. 1, illustrating a schematic diagram of a conventional MEMS region and a non-MEMS region. As shown in FIG. 1, a die 100 includes a MEMS region 104 and a non-MEMS region 102. A variety of MEMS devices 106 are fabricated in the MEMS region 104, for example, a vibration membrane or a motor. The non-MEMS region 102 includes a logic region, a memory region or a periphery circuit region and a variety of semiconductor devices are disposed therein (not shown), such as some active or inactive components. The surface of the non-MEMS region 102 includes a plurality of pads 108. The semiconductor devices in the non-MEMS region 102 or the MEMS device 106 in the MEMS region 104 can be driven by an outer signal through the pads 108 to carry out the input/output signal processing.
When fabricating the MEMS device 106, at least an etching process is provided to the die 100 after finishing all the MEMS device 106, the semiconductor devices and the metal interconnections. An etching gas such as HF, an etching solvent or other etchants is supplied to etch away the IMD layers in the MEMS region 104 and to form a variety of movable or mechanical MEMS devices 106 having 3D micro structures.
However, many problems occur during the etching process. For instance, in order to prevent the semiconductor devices in the non-MEMS region 102 from being damaged during the etching process, a mask layer (not shown) is usually provided on the non-MEMS region 102 to protect the IMD therebelow. The mask layer is usually a metal layer. However, entirely covering the conductive mask layer onto the non-MEMS region 102 will make each pad 108 electrically connect to each other and an electrical short phenomenon occurs. On the other hand, if the pad 108 is not covered by the mask layer, the etchant easily penetrates along the edge of the pad 108 and damages the devices in the non-MEMS region 102. Moreover, while the pad 108 is designed to drive the MEMS device 106 or the semiconductor device, the connection arrangement should also be taken into consideration, so as to avoid the short phenomenon or the cross talk noise.